The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems are used to deposit and/or etch film on a substrate such as a semiconductor wafer. For example, the substrate processing system may perform chemical vapor deposition (CVD), plasma-enhanced (PE) CVD, atomic layer deposition (ALD), PEALD, etc. Deposition or etching may be performed by supplying a gas mixture including one or more reactants to a processing chamber.
To use liquid precursors as reactants in CVD and/or ALD type processes, the liquid precursor is initially vaporized and then transported to a surface of the substrate. The vaporized precursor should not contain any liquid droplets and should have a uniform concentration and accurate dose. Two basic methods are commonly used for vaporizing precursor. For example, a bubbler bubbles a carrier gas through liquid precursor usually at an elevated temperature. The liquid precursor evaporates and is carried away with the carrier gas. However, the bubbler provides a variable exposure surface of the carrier gas to the liquid precursor depending on flow and a liquid level in the bath, which causes variable vapor concentrations. The act of bubbling can also cause droplets and/or foam to form and may cause liquid to be transported by the vaporized precursor to the surface of the substrate.
Alternately, an evaporator may be used. In the evaporator, a small amount of liquid precursor flows onto a heated surface. The liquid precursor evaporates and is carried away via a pressure differential or using a carrier gas. However, the evaporator feeds liquid from a bulk source in very small amounts. The low flow rate is difficult to meter and deliver accurately. A liquid delivery system typically includes a liquid flow controller and a capillary tube. The liquid delivery system is subject to blockage and bubbles forming in the liquid, which also causes the vapor delivery concentration to vary.